Terrorist and extortion bombings have always been a problem for law enforcement officials, not only on a national scale but on an international scale as well. One of the problems heretofore faced has been the manner of disposing of a detected bomb or explosive or similar device. In the more common instances, the bomb or explosive device is placed in a public place or in a vehicle parked in a public place. Upon detection, the problem arises as to disposal of the device. In past years the procedure typically has been for trained bomb disposal personnel to attempt to disarm the device on the site. There are cases, however, in which the device may be quite sophisticated, or cases in which trained personnel are not available, or where the device may be remotely controlled.
More recently the potential for serious injury or death of those attempting to disarm the explosive device has led to the use of video camera carrying robots which are brought close to the explosive device to determine its size, construction or other information which may assist in the safe deactivation of the device. Unfortunately, however, not all law enforcement groups can afford the expense of robot units and there are situations in which robots may not be suitable for their intended function. For example, a robot may not be able to disarm a bomb in a briefcase left in the open. In such a case, the use of a robot normally involves picking up the device and carrying it to a disposal vehicle in which the device is transported to a remote bomb disposal site. Should the device detonate during transport by the robot to the disposal vehicle, there is a potential for significant injury to those in the area as well as significant property damage in the immediate area.
Perhaps the largest single cause of bodily injury in detected explosive devices comes from blasts which take place as the law enforcement officials first on the scene attempt to disarm the bomb in order to protect the public and the surrounding property. There are instances in which the nature of the explosive device is such that it is not readily capable of being deactivated at the site, but where it is attempted to disarm the device in order to protect the surrounding property. In some cases, the procedure is to detonate the device on site by the use of a smaller explosive device used to set off the main charge of the bomb. The result is a blast which may cause significant property damage in the immediate area. In other cases, the smaller device is used in an attempt to deactivate the main explosive device, by destroying wires or disabling the detonation mechanism. The latter procedure, however, may result in detonation of the main device and a more powerful blast. Even if successful, the detonation of the smaller charge may cause damage to valuable property in the immediate vicinity. Timer controlled or remote controlled devices add still another complexity to deactivation of the explosive device, that is, the need to act both quickly and with precision.
Typically, the damage done by the explosion comes from two sources, the first being the compression wave of the blast and the second being the fireball which immediately follows the blast. The compression wave is usually a high amplitude, short duration compressive wave which moves radially outwardly in all directions from the source. The strength of the wave and its duration are a function of the power and amount of the explosives used in the device. The fireball is a result of combustion of the combustable materials in the immediate region of the blast and is almost immediate with the compressive wave. Since the fireball consumes the combustibles in the region of the device, the effect is a reduction in the pressure behind the compressive wave with the net effect that there is a high pressure overpressure by the compression wave followed almost immediately by a reduced pressure front. The fireball also operates to ignite the combustibles which are in the immediate vicinity. For example, in a bomb placed in a vehicle having fuel in the gas tank, the compressive wave may cause significant structural damage to the vehicle, including rupture of the fuel tank, if the explosive is powerful enough. The fireball may ignite the interior of the vehicle if there is combustible material present and may cause either a secondary explosion as the fuel detonates or a severe fire as the fuel ignites. The result is that the region around the vehicle is traversed by debris blown by the blast, followed by a secondary explosion or intense fire.
For relatively small devices, such as letter bombs and briefcase bombs it may be possible to use blast blankets placed over the device to inhibit the effects of the blast as the device is detonated on site. The difficulty with bomb blankets is that they are quite heavy, usually formed of flexible closely woven steel mesh and not easily transportable to the needed site. The weight of the blast blankets may be such as to require the use of a crane. Moreover, blast blankets are not usually available quickly. In the case of bombs placed in vehicles, the number of blast blankets needed to cover the entire vehicle may be more than is immediately available, even if there is available equipment to position the blanket.
It is also known that explosive materials are used in building clearance programs in which relatively large structures, sometimes in populated areas, are felled by explosive charges placed at strategic locations in the main support structure and usually detonated in a timed sequence. While those engaged in this type of building demolition are highly trained and exercise an unusual amount of care, occasionally problems do arise. Typically, the charges are set and when detonated, the structure collapses as planned, but sometimes there is a substantial amount of window breakage in the structures in the surrounding area. Normally, the explosives used in these types of operations tend not to produce a fireball, but do produce a significant compression wave. Further, since the charges are usually set at ground level, there may be significant window damage at street level.
As is apparent, it would be desirable to provide a system which absorbs the compression wave so as to reduce the structural and bodily injury caused by the blast over-pressure while significantly reducing the fireball so as to reduce the damage caused by the combustion of ingitable or explosive material in the immediate vicinity of the blast. Particularly advantageous would be a system which is readily mobile, easy to use, effective for the purpose intended and which supresses the fireball as well as the effect of the compressive wave.
It is known in the prior art to use foams in fighting fires. Typically such foams are formed from water-soluble surfactants of the perfluorocarbon type which may be dispensed from a variety of different types of equipment, all well known in the art. One such typical material is known in the art as AFFF, see U.S. Pat. Nos. 3,258,423; 3,562,156 and 3,772,195, for example. Generically these materials are also known as FCS and HCS materials, e.g., fluorocarbon surfactants and hydrocarbon surfactants. Variations include those AFFF compositions which include a fluoro-chemical synergist known as F-amide and an FCS called F-AMPS, see for example U.S. Pat. Nos. 4,090,967 and 4,014,926. These foam producing materials are known to produce high-expansion foams which are known to spread over the surface in order to suppress vaporization of gasoline, which is the principal reason these materials were developed. Other patents which disclose similar materials are U.S. Pat. No. 4,090,967, United Kingdom Pat. No. 1,230,980 of 1971 and No. 1,126,027 of 1968, and Canadian Pat. No. 842,252, for example.
Foams from the above and other equivalent materials tend to be of small envelope or bubble size and flowable, the latter being one of the desirable qualities for use in fighting fires. Moreover, the foams may be formed relatively easily at the site of application by any number of different devices, all well known in the art. Portable units of various sizes as well as truck mounted units are commercially available for forming and dispensing various amounts of foamed material. For example, units are available which dispense from 2,000 to 15,000 or more cubic feet of foam per minute. Dispensing units include water reaction motors, electrically powered units, turbine units, compressed gas driven units and the like. Some of the dispensing equipment includes a tubular member which may be from two feet to ten feet in diameter, connected to the foam generator, and used to control the direction of foam discharge. The foam is discharged from the open end of the tubular member remote from the foam generator. The result is that an enormous amount of foam may be quickly dispensed from a relatively small unit in a relatively short time using a relatively small amount of water and foaming agent. Since the foam includes a surfactant, it tends to flow easily and spread quickly over the contact surfaces which it readily wets. Such foams may also be dispensed from high velocity nozzles and projected a relatively long distance and with sufficient accuracy to reach a designated target area.
Typically, the foams above described are sometimes referred to as expanded foams, having an expansion ratio of 50 to 1 to 1000 to 1. These types of foams do not have sufficient strength to remain in a three-dimensional shape, for example, a mound, for any significant length of time. Where the foam is dispensed from a tubular member, customarily referred to as a chute, the chute may be of a length of one hundred feet or more, with the foam being dispensed from the open end of the chute remote from the generator. Generators are known which have an output or discharge opening which may vary from one square foot to as much as twenty-five or more square feet.
The foams described, dispensed by known equipment and techniques, tend to have a relatively long life since collapse of the foam is due principally to evaporation of the water component of the foam. Thus in the absence of heat or flame, the foam tends to remain fairly stable for a relatively long period. However, it is also true that the foam tends to spread laterally rather quickly since this is one of the desirable features in its use as a fire-fighting material.
It is believed to be known in the prior art that fire fighting foams do exhibit blast suppression qualities. Even though known, there appears to have been little practical use of foams as a blast suppression medium apparently because of the inability to deliver the foam to the desired location and to maintain the foam in the immediate region of the explosive device. In other words, there does not exist in the prior art a methodology for containing the foam in the desired location, nor was it apparently recognized that the key to the successful use of foams as a blast suppression medium was dependent upon confining the foam. As near as can be determined, little use has been made in open areas, such as streets, large rooms and the like, of foams as a blast suppressor because it may not have been recognized that the effectiveness of the foam as a blast suppressor could be significantly increased by confining the foam.